Primarily, the proposed work centers on the application of dialysis culture and continuous culture to studies of the physiology of bacteria in dental plaque. A major aim of the work will be to simulate plaque growth conditions in vitro and to define the physiologic responses of bacteria in crowded conditions to changes in environmental factors such as nurtient supply, pH, Eh, pCa and phosphate level. Special attention will be paid to the interactions of calcium ions with plaque bacteria, including wall and membrane stabilizing effects of the ions, uptake of calcium into the cell with intracellular calcification, competition between calcium and magnesium ions for sites within cells and the capacities of calcium ions to induce a type of cryptobiotic state in plaque bacteria. Both dialysis cultures and gelled continuous cultures will be used to test the hypothesis that bacteria in plaque are in a situation in which most of the ATP produced by catabolic processes is used for maintenance and little is used for growth. The effectiveness of antimicrobial agents in controlling bacterial metabolism under these circumstances will be tested with the aim of applying this knowledge to the alleviation of dental caries and possibly periodontal disease.